1. Field of the Invention
This invention is directed to computer systems, in general, and to computer systems which include a plurality of processor circuits which utilize a common memory unit or device, in particular.
2. Prior Art
There are many known computer systems available to the art. Typically, the computer systems are designed to achieve optimum operating characteristics which characteristics vary as the art improves. The optimum designs include various alterations in terms of the operation, the speed, the throughput, and the like, generally in an attempt to maximize the system operation relative to the cost thereof.
The maximization of operation versus cost is frequently a trade-off in one or more parameters. In some occasions, the trade-off is in the hardware versus firmware (software) applications. That is, sometimes greater use is made of the firmware or software while in other applications greater use is made of hardware, especially dedicated hardware.
Also, in many systems arrangements are made wherein a plurality of processor units are utilized. The processors may be central processing units (CPU's) or they may be other processors such as micro-processors, mini-computers or the like. By utilizing a plurality of these processing units, different capabilities of different processors can be utilized together. In addition, processors having different word lengths (16-bits, 8-bits, or the like) can be utilized in a single system. This permits greater flexibility in operating parameters and characteristics.
However, it has typically been a problem that utilization of more than one processor requires extensive software interconnections or control in order to assure that the appropriate processor is functioning at the appropriate time. This has created the problem that extensive memory or software operations are required which reduces the other operating parameters of the overall system. In addition, the software application is usually such that a relatively slow operation occurs. That is, it is required that the software produce a checking function to determine which processor is in operation, then a selection operation to select which processor should be in operation, and then other housekeeping or administrative controls to assure that the appropriate processor is functioning at the appropriate time and the other processor is not improperly operating, and so forth. This software control is, as noted, relatively slow and uses up much of the system memory.